Ecohydrologic coevolution in drylands: relative roles of vegetation, soil depth and runoff connectivity on ecosystem shifts.

Degradation in drylands is often triggered by shifts induced by feedbacks between coevolving hydrology, vegetation, soils and geomorphic processes. These feedbacks affect the redistribution of surface runoff and therefore the emergent patterns of vegetation and landscape connectivity. Existing theories explaining ecohydrology shifts in semiarid areas with patchy vegetation focus on biomass-water interactions but do not explicitly account for feedbacks with evolving landform and soil depths. Here we study the observed ecohydrologic response of patchy semiarid areas in Australia and Spain, analysing interactions between PFTs traits and landform processes.

We further use a mechanistic modelling framework to investigate the role of coevolving soil depths on the stability and resilience of these systems. We find that areas with deeper soils tend to display more regular vegetation patterns and their resilience and recovery after an initial disturbance are strongly affected by plant facilitation strategies. However for ecosystems in steep areas, feedback effects with landforms become stronger, and sudden changes in connectivity can easily lead to degradation. In contrast, we show that for shallow soils, plant facilitation effects become less important and vegetation patterns are irregular. In this case, soil depth becomes the key factor prescribing surface connectivity and recovery of the system after disturbance. These results have critical implications for effective management and restoration efforts, and for understanding the effects of changes in climate and land use.